1. Field of the Invention
The present invention relates to a radiographic image processing device and a radiographic image processing method which perform a noise removal process for removing quantum noise included in a radiographic image and a program which causes a computer to perform a radiographic image processing method.
2. Description of the Related Art
In recent years, when diagnosis is performed using a radiographic image of a subject, image processing, such as a frequency enhancement process and a gradation process, has been performed for a captured radiographic image to change the radiographic image to an image suitable for diagnosis and the image has been displayed on a display device, such as a liquid crystal monitor, or has been output as a hard copy on a film. Here, a radiographic image has the problem that quantum noise of radiation is noticeable in a portion in which a radiation dose is small and density is low. Therefore, as image processing for a radiographic image, various methods have been proposed which perform a noise removal process for reducing or removing quantum noise included in a radiographic image.
For example, a smoothing process which uses a smoothing filter for removing a frequency component corresponding to quantum noise is known as the noise removal process. For example, JP2002-133410A discloses a method which performs frequency conversion for a radiographic image to create a band image indicating frequency components in different frequency bands, detects an edge direction of a pixel of interest to be processed in the band image, performs a smoothing process along the edge direction, performs frequency synthesis for the band image subjected to the smoothing process, and acquires a processed radiographic image. The use of the method disclosed in JP2002-133410A makes it possible to remove noise included in the radiographic image, without the deterioration of an edge component in the radiographic image.
During the capture of a radiographic image of a subject, when the thickness of the subject is too large, radiation is scattered in the subject and the contrast of the acquired radiographic image is reduced due to the scattered radiation (hereinafter, also referred to as scattered ray). As such, when a gradation process which enhances contrast or frequency processing which enhances a frequency component of an edge portion included in the subject is performed for the radiographic image of which the contrast has been reduced, it is possible to reduce the influence of scattered radiation and to obtain a high-quality radiographic image suitable for diagnosis.